Magnetic recording tapes, disks and cards comprise a non-magnetic base such as a polyester or polycarbonate film on which is coated a magnetic layer composed of ferromagnetic particles dispersed in a binder resin.
Although iron oxide particles were used in the earlier magnetic tapes and ferric oxide is still commonly used, metallic iron particles offer important advantages for high energy or high density magnetic recording materials. Metallic iron particles have higher magnetizations than ferric oxide, they can be made smaller than oxide particles without risking paramagnetization and their coercivity is high. Unfortunately, the metallic particles are highly reactive with oxygen and moisture and will quickly corrode when exposed to air and moisture and the recording properties will deteriorate. Numerous attempts have been made to provide coatings to protect against oxidative corrosion, but all have drawbacks. A need has existed for a better method of protecting iron and iron alloys in general against corrosion and especially for a method that can be employed in the manufacture of recording materials which have a coated magnetic layer of iron or iron alloy particles dispersed in a binder resin.